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System identification of feedback in hearing aids.
J Hellgren1, T Lunner, S Arlinger
1Department of Neuroscience and Locomotion, Linköping University, Sweden. johan.hellgren@oto.liu.se
The Journal of the Acoustical Society of America
|June 25, 1999
Summary
Understanding hearing aid feedback is crucial. This study models acoustic feedback paths, identifying vent and earmould leaks as dominant factors, to determine maximum usable hearing aid gain.
Area of Science:
- Audiology
- Acoustics
- Biomedical Engineering
Background:
- Hearing aid feedback, or 'howling,' limits device gain and user satisfaction.
- Existing models do not fully capture the complex acoustic feedback paths in various hearing aid types.
Purpose of the Study:
- To investigate and model acoustic feedback paths in Behind-the-Ear (BTE), In-the-Ear (ITE), and In-the-Ear-Canal (ITEC) hearing aids.
- To determine the maximum gain achievable before feedback occurs for different hearing aid categories.
Main Methods:
- Defined an acoustic feedback equivalent (AFE) transfer function from ear canal to hearing aid microphone.
- Measured AFE magnitude and phase responses in ten human subjects and a KEMAR manikin.
- Modeled the AFE using a fourth-order filter with a delay.
Main Results:
- Acoustic feedback via the vent and earmould-ear canal leak significantly dominated the AFE.
- The model showed good agreement with measured AFE data across subjects and the KEMAR.
- Identified transfer functions were used to calculate maximum real ear aided gain (REAG).
Conclusions:
- The developed AFE model accurately represents acoustic feedback mechanisms in BTE, ITE, and ITEC hearing aids.
- Vent and earmould leakage are critical factors influencing hearing aid feedback and maximum gain.
- This research provides a foundation for optimizing hearing aid gain and reducing feedback.